1. Field of the Invention
The invention relates generally to the storage of data on magnetic recording tape, and more specifically, to the storage of digital data in helical format on a magnetic tape housed within a single reel tape cartridge.
2. Related Art
The data processing industry stores large amounts of digital data on magnetic tapes. The 3480 tape cartridge (developed by IBM Corporation, Armonk, N.Y., U.S.A.) is an industry standard for magnetic storage media. The 3480 cartridge is a single reel cartridge with a length of xc2xd inch wide magnetic tape stored on it. The cartridge housing protects the tape from damage while allowing the tape reel to be driven from a drive mechanism on the underside of the cartridge housing. The tape is withdrawn from an opening formed at one corner of the cartridge. A leader block attached to a free end of the tape allows the tape to be withdrawn from the cartridge for read/write operations.
Read/write operations are performed by a tape xe2x80x9ctransport.xe2x80x9d The standard tape transport accepts the tape cartridge into an elevator assembly. A threading mechanism grabs the leader block and pulls it free from the cartridge. The leader block is then used to thread the tape through a series of guide posts, across a longitudinal read/write head, and into a slot in a take-up reel. Once threaded, the tape from the cartridge can be driven across the read/write heads for data transfer operations.
The standard 3480 cartridge contains 541 feet of tape. Data is stored on the tape in an 18 track format, typically providing approximately 200 MB (megabytes) of data storage capacity.
For automated storage and handling of large numbers of 3480 cartridges, automated mass storage systems have been developed. For example, the 4400 automated cartridge system (ACS) from Storage Technology Corporation, Louisville, Colo., U.S.A., is capable of storing up to 6,000 3480 cartridges. The 4400 ACS can quickly locate a selected cartridge and load it into a cartridge transport for read/write operations. The Model 4400 ACS typically has between one and four cartridge transports associated with it.
The 4400 ACS has proven to be a cost-effective data storage system. With each of 6,000 cartridges providing 200 megabytes of storage capacity, one 4400 ACS has a total capacity of 1.2 terabytes (1.2xc3x971012 bytes). This storage capacity is provided in a unit that occupies approximately 100 square feet of floor space. Nevertheless, it is desirable to increase the storage density of the 4400 ACS.
Data is currently stored on a 3480 cartridge in an 18 track longitudinal format. However, it is known in the industry that using a helical scan data storage format would allow approximately a 100 times increase in storage capacity. In other words, the typical 3480 cartridge would have a helical scan storage capacity of 25 gigabytes rather than the 200 megabytes of the longitudinal format. At 25 gigabytes per cartridge, the 4400 ACS would provide a total storage capacity of 150 terabytes. Thus, helical-scan technology holds promise for increasing the storage capacity of the 4400 ACS by a factor of greater than 100 by simply changing the format with which data is stored in each tape cartridge.
Changing the data storage format for a cartridge necessitates that a new transport be developed. Helical scan transports have gained widespread use in the video industry. However, a helical-scan transport for a one-half inch tape cartridge is not currently commercially available.
The helical scan transport is quite different than the longitudinal style transport. The helical scan transport includes a cylindrical rotating head around which the tape must be wrapped for read/write operations. The helical scan tape path is much more complex than the path for longitudinal transports.
The video industry has adopted a two reel magnetic tape cassette as its standard media. Loading of the tape from a cassette through the tape path of a helical scan transport is straightforward and well known in the art. The loading of tape from a cartridge through a helical scan tape path, however, is more difficult and has not been developed to the level of that for a cassette. Thus, two standard and distinct media form factors have developed for the video industry and the data processing industry. The form factors are incompatible. 3480 style cartridges cannot be used with the helical-scan cassette transports of the video industry.
One apparent reason for the data processing industry""s selection of the cartridge as its standard data storage media is volumetric economy. By not including a take-up reel, the cartridge is roughly one-half the size of a cassette for the same tape length. Thus, a cartridge has twice the storage capacity per unit volume of a cassette.
While a helical-scan transport is not commercially available for a one-half inch tape cartridge, one is described in commonly owned U.S. Pat. No. 5,128,815 to Leonhardt et al. Leonhardt et al. teach positioning a cartridge and a take-up reel in a helical transport so that a cassette is emulated. This simplifies tape loading. However, such a design would have a form factor incompatible with the 4400 ACS. That is, the physical layout and dimensioning would not allow the resulting transport to be used with existing 4400 ACS equipment without substantial modification. This is a critical concern in the computer and data processing industry. New technologies and advancements must be compatible with existing technologies. For example, to have maximum utility, a helical-scan transport must have a form factor compatible with the 4400 ACS environment.
An important feature of the form factor of such a transport is the frontal surface area. That is, the front face of the transport which contains the opening for accepting a tape cartridge must be small enough to interface with other equipment. Form factors such as that disclosed by Leonhardt et al. in the ""815 patent may have too large a frontal area for many applications because of the side-by-side arrangement of the cartridge and the take-up reel.
What is needed is a helical scan transport which can store data on and retrieve data from a 3480 or similar data cartridge and which has a form factor compatible with existing data storage systems (e.g., the Storage Technology Corporation Model 4400 ACS).
The invention is a helical scan transport for a magnetic tape cartridge. The transport has a substantially linear tape loading path and a form factor which allows its use with a Storage Technology Corporation Model 4400 automated cartridge system (also known as a data cartridge storage xe2x80x9clibraryxe2x80x9d). A new helical scan tape cartridge was developed for use with the transport of the invention. The helical cartridge has a form factor similar to the 3480 style cartridge. Thus, the 4400 ACS can store both the helical cartridges and the 3480 style cartridges. By producing a helical scan transport and helical cartridge which are compatible with existing automated cartridge systems, the data storage capacity of existing systems can be vastly increased without the need for retrofitting or otherwise modifying existing systems.
The helical scan transport apparatus of the invention includes a chassis having a front end portion and a rear end portion. An elevator assembly is mounted on the chassis at the front end. The elevator assembly is configured to receive a tape cartridge and to position the tape cartridge in a loaded position. A take-up reel assembly is coupled to the chassis at the rear end portion. A helical deck is mounted on a central portion of the chassis between the elevator assembly and the take-up reel assembly. The helical deck includes a rotary read/write head, a substantially linear tape loading path between the elevator assembly and the take-up reel assembly, and movable guides for seizing the tape from the tape loading path and for at least partially wrapping the tape around the rotary head. A linear threading mechanism is configured to grasp the leader block of the tape, thread the tape through the tape loading path of the helical deck, and couple the leader block to the take-up reel assembly.
In the preferred embodiment, the helical deck is taken from a commercially available Panasonic Model D350 digital video cassette recorder. Also in the preferred embodiment, the helical transport is dimensioned to fit within a rectangular enclosure measuring approximately 12.5xe2x80x3 (inches) wide by 26.5xe2x80x3 deep and configured such that a plurality of the transport apparatuses may be stacked within the enclosure with a vertical spacing of 11.06xe2x80x3 on center. The front end portion of the chassis extends 7.0xe2x80x3 outward from the enclosure and is configured to mate with the 4400 automated cartridge system when the enclosure is coupled to a housing of the 4400 automated cartridge system.
The rectangular enclosure is a frame assembly configured to enclose up to four of the helical transports of the invention. The enclosure measures 26.5xe2x80x3 inches deep by 28.0 inches wide by 67.775 inches high (not including castors). The enclosure houses each transport and its associated electronic circuitry in a side-by-side arrangement. The transport fills approximately 12.3xe2x80x3 of the width and the remaining width is available for a power supply and the electronic circuitry associated with the transport.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.